When biologists first spied captive-bred California condors eating a dead sea lion that had washed up on the Big Sur coast, they were thrilled.

“They were foraging on their own, which was a big step in the right direction for recovery of this species,” said Joe Burnett, senior wildlife biologist with Ventana Wildlife Society.

Burnett has spent many a night hiking into the backcountry of Big Sur, carrying carcasses to leave for these endangered scavengers in an attempt to mimic natural conditions. Following this initial feast in 1999, Big Sur condors began feeding on beached marine mammals more and more each year. By 2006, their most common food source was California sea lions.

“In the mid to late 1800s, condors were documented in Monterey Bay foraging on marine mammals,” said Burnett. “So we suspected and hoped they’d develop the same pattern.”

But what they didn’t count on was that, along with nutrients and energy, condors would ingest harmful levels of marine contaminants. Now, preliminary reports suggest that these contaminants — including residues from the banned insecticide DDT — are affecting the already tenuous reproductive success of the flock.

“We had our first known nesting in 2006 in the burned out cavity of a redwood tree 60 feet above the ground,” said Burnett. Though researchers initially observed characteristic nesting behavior, there was no sign that a baby had hatched. “We suspected the birds had laid an egg and something had Advertisement happened … (so) a biologist from the U.S. Fish and Wildlife Service climbed up in the tree. He sifted through the substrate in the bottom of the nest and found egg shell fragments. This put it on our radar.”

It’s been well documented in scientific literature that DDE, the metabolic breakdown of DDT, which was banned by the FDA in December 1972, causes egg shell thinning in many birds species, including bald eagles, ospreys, peregrine falcons and brown pelicans. So when Burnett saw the shell fragments, his suspicions were immediately aroused.

“When you see egg shell thinning, all scientific data points to DDE. So that threw up a red flag,” said Burnett.

The following year, biologists began to collect all the wild-laid eggs they could find and swap them out with captive-bred eggs from the Los Angeles Zoo. While unsuspecting wild condors raised chicks hatched from captive-bred eggs, the wild-laid eggs were closely monitored to ensure survival. Working in conjunction with USFWS, Ventana began to collect data on these wild-laid eggs, comparing egg shells and tissues from this coastal population of condors to those of condors from the Southern California flock. Unlike the Big Sur birds, members of the Southern California flock are released more than 40 miles inland near the foothills of the southern Sierra Nevada mountains, where they don’t encounter marine mammals as a food source.

Although the study is ongoing, Burnett said that preliminary results suggest that eggshells from the Big Sur flock were substantially thinner than those found down south. Early indicators suggest DDE as the principle cause.

The condors being studied are feeding at a California sea lion haul-out in Big Sur, at the base of a 100-foot cliff with steep terrain that generates wind uplift — the perfect marriage of conditions for condors. The only problem is that the sea lions that rest there, and occasionally die and wash ashore, breed in Southern California at a Channel Island rookery amid some of the most DDT-contaminated waters in the world.

In the 1950s and 1960s, these breeding grounds were a dump site where the Montrose Chemical Corporation, the world’s largest manufacturer of DDT at the time, dumped hundreds of tons of DDT-contaminated waste into the ocean. One of the reasons this chemical was so popular as a pesticide is also one of the reasons it is so dangerous to wildlife — it persists in the environment for an extremely long time. When the U.S. Geological Survey monitored marine sediments in this area in the 1990s, they found that more than 100 metric tons of DDT still remained.

Another characteristic of DDT that makes it dangerous to wildlife is that it is stored in animals’ fat cells after it is ingested. This causes the chemical and its metabolites to accumulate in species throughout the food web. When animals low on the food chain are eaten by animals higher on the food chain, the contaminant becomes more concentrated in the predators’ fat cells.

So, in the case of California sea lions, invertebrates living in DDT-contaminated sediments ingest the chemical and are then eaten by small fish. Small fish are in turn eaten by bigger fish, and so on, until sea lions, at the apex of the food chain, consume enormous amounts of fish and, consequently, enormous amounts of the contaminant.

When the sea lions leave their breeding grounds, they travel up the coast of California, where many stop off at the haul-out in Big Sur. One of the few animals feeding higher on the food chain than sea lions is the California condor.

Even if DDT levels aren’t high enough to kill condors outright, Burnett pointed out that depressing their reproductive success is essentially a death sentence — especially in an animal that takes seven years to reach sexual maturity and only produces one egg every two years.

“There is no baseline for the level of marine contaminants that condors can sustain,” said Burnett. “All we have are data for peregrine (falcons) and bald eagles.” DDT intake by falcons and eagles is minimal in comparison. Ventana is looking at egg tissues, and preliminary data suggests that DDE levels are higher than in bald eagles that were affected by DDT.

“The levels thus far are alarmingly high,” Burnett said.

Ventana has used the successful bald eagle restoration project on Santa Catalina Island as a template for the condor study. In the 1980s, the Institute for Wildlife Studies in collaboration with USFWS started to release eagles onto Santa Catalina Island, near the Montrose dump site. The first eggs laid in 1987 broke before they hatched, alerting biologists to the possibility of DDT contamination. Thus, IWS initiated an ecotoxicology study, linking thin egg shells in eagles to prey sources contaminated from DDT residues.

Though the condor team is still in the throes of discovery, Burnett said, “We are in process of making the link to the same point-source that’s been hindering the population of bald eagles.” The good news about this point-source is that levels of DDT appear to have declined, albeit slowly, through the decades.

“We have definitely seen levels (of DDE in egg tissues) decrease from the 1990s to the mid-2000s,” said David Garcelon, founder of the Institute of Wildlife Studies and principle investigator of the eagle project. “The trend has definitely gone way down. It’s now low enough for (eagles) to hatch eggs.” The situation for eagles is different from condors since eagles primarily prey on fish, which are lower on the food chain and have less contamination. Still, the bald eagle situation illustrates that mitigating the issue of DDT contamination is primarily a waiting game — a daunting prospect for a nonprofit group trying to keep the flock intact.

“There aren’t any new sources of DDT in North America, so we’re trying to wait out the persistence of DDT put out there before,” said Garcelon. “It’s difficult to say how long it will last. There’s still a lot in river bottoms and in the bottom of the ocean. With no oxygen, things break down really slowly.

“But based on what we’ve seen with bald eagles, and how it’s turned around in a short period of time, I certainly wouldn’t give up on condors based on a fear of marine contaminants. I’m not sure how long it will take for condors to start hatching successfully on their own, but I certainly wouldn’t give up.”

In the early 1900s, condors ranged along the entire Pacific Coast, from British Columbia to Baja California. Fossil evidence shows their prehistoric range was throughout the southern United States, down into mainland Mexico and even up into New York.

These obligate scavengers provide a necessary ecosystem service by eating dead animals and recycling their energy back into the ecosystem.

Condors can travel distances of up to 150 miles searching for carrion.

They use visual cues to locate food and, once found, will circle the sky above as a signal to other condors that a food source has been located.

Their scientific genus name, Gymnogyps, is Greek for “naked vulture,”” referring to this species’ naked head, neck and feet. This is an adaptation that allows the bird to stay relatively clean while feeding from the body cavity of a dead animal.

Condors have ridges on their tongues that correlate with grooves on the top of their mouths “” they perfectly fit together to form a straw-like structure, an adaptation for feeding.

These animals reach sexual maturity only after 6-8 years, and they can live up to 50 or 60 years.

Condor pairs mate for life.

Females usually lay only a single egg every other year (but they will often lay a second or third if the first one is removed or falls from the nest).

Both males and females share in incubating eggs, as well as care and feeding of young. · Condors were listed as endangered under the Federal Endangered Species Act in 1967.

As recently as the 1980s, there were only 22 California condors left in the world. In 1987, the last wild condor was captured and taken into captivity. Since then, captive breeding programs have been successful in hatching baby chicks and releasing them to reestablish wild populations.

The total California condor population, including wild and captive birds in California, Arizona and Baja California, is now more than 300.

Despite the regional ban throughout condors” range in southern and central California, the main threat to adult California condors today is poisoning by ingestion of carrion tainted from lead ammunition.

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